docs: Added Shiny for Python example (#74)

Shiny for Python app using the SDK to access Databricks

examples/connect/shiny-python/README.md

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+# Shiny for Python Example
+
+## Start the app locally
+
+```bash
+shiny run app.py
+```
+
+## Deploy to Posit Connect
+
+Validate that `rsconnect-python` is installed:
+
+```bash
+rsconnect version
+```
+
+Or install it as documented in the [installation](https://docs.posit.co/rsconnect-python/#installation) section of the documentation.
+
+To publish, make sure `CONNECT_SERVER`, `CONNECT_API_KEY`, `DATABRICKS_HOST`, `DATABRICKS_PATH` have valid values. Then, on a terminal session, enter the following command:
+
+```bash
+rsconnect deploy shiny . \
+  --server "${CONNECT_SERVER}" \
+  --api-key "${CONNECT_API_KEY}" \
+  --environment DATABRICKS_HOST \
+  --environment DATABRICKS_PATH
+```
+
+Note that the Databricks environment variables do not need to be resolved by the shell, so they do not include the `$` prefix.
+
+The Databricks environment variables only need to be set once, unless a change needs to be made. If the values have not changed, you don’t need to provide them again when you publish updates to the document.
+
+```
+rsconnect deploy shiny . \
+  --server "${CONNECT_SERVER}" \
+  --api-key "${CONNECT_API_KEY}"
+```

examples/connect/shiny-python/app.py

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+# -*- coding: utf-8 -*-
+# mypy: ignore-errors
+import os
+
+import pandas as pd
+
+from posit.connect.external.databricks import viewer_credentials_provider
+
+from databricks import sql
+from databricks.sdk.service.iam import CurrentUserAPI
+from databricks.sdk.core import ApiClient, Config
+
+from shiny import App, Inputs, Outputs, Session, render, ui
+
+DATABRICKS_HOST=os.getenv("DATABRICKS_HOST")
+DATABRICKS_HOST_URL = f"https://{DATABRICKS_HOST}"
+SQL_HTTP_PATH = os.getenv("DATABRICKS_PATH")
+
+app_ui = ui.page_fluid(
+    ui.output_text("text"),
+    ui.output_data_frame("result")
+)
+
+def server(input: Inputs, output: Outputs, session: Session):
+    """
+    Shiny for Python example application that shows user information and 
+    the first few rows from a table hosted in Databricks.
+    """
+
+    session_token = session.http_conn.headers.get('Posit-Connect-User-Session-Token')
+    credentials_provider = viewer_credentials_provider(user_session_token=session_token)
+
+    @render.data_frame
+    def result():
+
+        query = "SELECT * FROM samples.nyctaxi.trips LIMIT 10;"
+
+        with sql.connect(server_hostname=DATABRICKS_HOST,
+                         http_path=SQL_HTTP_PATH,
+                         auth_type="databricks-oauth",
+                         credentials_provider=credentials_provider) as connection:
+            with connection.cursor() as cursor:
+                cursor.execute(query)
+                rows = cursor.fetchall()
+                df = pd.DataFrame(rows, columns = [col[0] for col in cursor.description])
+                return df
+
+    @render.text
+    def text():
+        cfg = Config(
+            host=DATABRICKS_HOST_URL, credentials_provider=credentials_provider
+        )
+        databricks_user_info = CurrentUserAPI(ApiClient(cfg)).me()
+        return f"Hello, {databricks_user_info.display_name}!"
+
+app = App(app_ui, server)

examples/connect/shiny-python/requirements.txt

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+databricks-sql-connector==3.0.1
+databricks-sdk==0.20.0
+shiny==0.7.1
+git+https://github.com/posit-dev/posit-sdk-py.git